How do things dull?

[Pete Simmons]

OK - We all study getting things sharp.

Do Not laugh but how do they get dull?

Any wood is many times softer than any steel yet the wood seems to be able to change the shape of the blade.

If we used a sharp HSS blade for a month cutting slices of cooked meat in a Deli would the shape of the blade erode or change?

How about a month of cutting Jello Squares???

Or are there small impurities in the soft wood (like very small pieces of sand) that over time wear away at our nice sharp blades??

[Jim Becker]

"Wood" the material is "relatively soft" compared to the metals used for cutting tools, but the fibers and minerals contained within the wood have abrasive qualities that will wear the cutting edge. The heat from friction will also contribute to the process.

[Gary Keedwell]

Wear n' tear my fellow. Even water will round a rock after enough time.(river rocks) Heat is another big factor. A machinist can mill stainless steel all day long as long as the coolant (water) stays on the end mill (cutter). Run the end mill (cutter) without coolant (dry) and it will get hot and then lose it's temper and edge and get dull.
That is why you shouldn't take too big if a cut with your router . Take mutiple passes and your router bits will stay cooler, hence, sharper..longer.
DAMHIKT ( don't ask me how I know this):D
Gary K.

[Pete Simmons]

OK - I buy the heat part but.....

Would "Pure Water" NO minerals or any oter contaminate, wear a rock down over time?

I would guess that if the Colorado River did not carry large amounts of sand with it as it flows the Grand Canyon might still be a small river.

[Lee DeRaud]

Would "Pure Water" NO minerals or any oter contaminate, wear a rock down over time?Yes, for some extremely large value of "time", assuming an isolated/stationary rock. But most of the rounding/smoothing of river rocks is due to them tumbling over each other and/or sand on the bottom of the river due to the current. Pure water can erode rock if freeze/thaw cycles occur, but that's a different mechanism.

Personally I blame the whole thing on Microsoft and Bill Gates' greed...oops, sorry, wrong thread.

[Andrew Williams]

Personally I have found that microscopic rusting is a big reason why things get dull. I can understand a plane iron or chisel getting dull from pushing it through wood, but some of them get dull just sitting on the shelf. Maybe not quite so fast, but they do.

[Gary Keedwell]

:rolleyes:
OK - I buy the heat part but.....

Would "Pure Water" NO minerals or any oter contaminate, wear a rock down over time?

I would guess that if the Colorado River did not carry large amounts of sand with it as it flows the Grand Canyon might still be a small river.
:rolleyes: Hey buddy, I believe "river water" was used as a reference, where did the "pure water" come from:confused: . Describe pure. You do have a good point, though.
Maybe different water would be more abrasive, such as salt water compared to "fresh water". Describe fresh water. How about clorinated water.......enough already!!!:p
Gary K.

[Christof Grohs]

"Wood" the material is "relatively soft" compared to the metals used for cutting tools, but the fibers and minerals contained within the wood have abrasive qualities that will wear the cutting edge. The heat from friction will also contribute to the process.

There is Silica and Calcium Carbonate, among other minerals, present in the cellular tissue. These minerals are present in all cellular tissue however some species have more than others. The same is true of grasses like bamboo and palm. Blades are no match for these minerals.

[Mike Henderson]

OK - I buy the heat part but.....

Would "Pure Water" NO minerals or any oter contaminate, wear a rock down over time?

I would guess that if the Colorado River did not carry large amounts of sand with it as it flows the Grand Canyon might still be a small river.
There is no such thing as "pure" water in nature. Rain picks up contamination as it falls through the sky. Additionally, each droplet requires something to condense around, and that's often a dust speck.

Once the water hits the ground, it dissolves a variety of minerals in the ground.

I agree with your comment about sand and other materials being carried in the water (but not dissolved by the water). Smaller rocks are abraided by the tumbling action of being moved by water, and the sand (and other materials) in the water act like an abrasive on the earth, especially where the water is moving fast. Time is also a factor - the erosion we see happened over thousands to millions of years.

Mike

[Cliff Rohrabacher]

Would "Pure Water" NO minerals or any oter contaminate, wear a rock down over time?
Absotively positutely


I would guess that if the Colorado River did not carry large amounts of sand with it as it flows the Grand Canyon might still be a small river.
Don't doubt that the freight of abrasives makes a difference. It does. But the water alone will do it also.

[Michael Schwartz]

Water is technically a solvent, so even without impurities it seems to me like it should also dissolve rocks over time as welll as with impurities erode them.

[mike holden]

Okay, now we all know water can wear down stone.
Back to the question of why wood wears down the steel of our cutting tools: remember that wood is cellular - think of lots of wooden fruit crates - further they are glued together by a substance that I think is called "lignin" - So on a microscopic level we have the blade of a caterpillar D8 smashing across a field of glued together fruit crates. At this level, I think one can see how there will be wear and tear on the cutting edge.

Just how I visualize it, YMMV
Mike

[Gary Keedwell]

Heat and friction....just like my boss wears me down.:(

Gary K.

[David Epperson]

Would "Pure Water" NO minerals or any other contaminate, wear a rock down over time?

Yep. Look at water jet cutting. Can cut steel and glass, works better WITH some entrained abrasives, but works without them as well.

[Lee DeRaud]

Yep. Look at water jet cutting. Can cut steel and glass, works better WITH some entrained abrasives, but works without them as well.For soft materials, yes.
(See http://www.waterjets.org/waterjet_glossary.html#Waterjet)

[Gary Keedwell]

http://www.dixmetals.com/NewsEvents/HighTechCutting.html?souce=google&gclid=COK8-qHD64wCFQQfgAodSVRY1A :)

Another one here.

Gary K.

[Eddie Darby]

If the metal has perfect bonds at the atomic level, then dulling would be a lot harder, but this is not the case. Metals contain what is called dislocations, which is a mis-alignment in the atom matrix.

This leads to a weakness in the metal that causes stresses to gather around. Get enough stress in that area, and you get more dislocations. More dislocations make for dulling when a piece falls off.

Just like a crack is a mechanism that focuses stress and concentrates it in one small area, a dislocation is a very small small small crack, which just happens to be very very good at concentrating stress. The smaller the better.

When blades are cryo frozen, it is in hope that the slowed down vibrating metal atoms will form more bonds, and thus last longer between sharpening because there are fewer dislocations.

[Lynn Sonier]

Intriguing thread, guys. Very informative.

[Bill White]

I'm gettin' a headache. Too much dulling effect I guess.
Bill

[Gary Keedwell]

I'm getting a headache, too. I think it is because I'm a dullard.:rolleyes: :D
Gary K.

[Rich Engelhardt]

Hello Pete,
Sharp edges curl over with use and appear dull.
A steel (such as a butchers steel) or a ceramic rod (like the Spyderco Sharpmaker - straighten the edge back into it's normal position.

Soft material such as wood or paper or cardboard turn the wafer thin edge down - they don't really wear away at it.
Here's the rub though. Once the edge has curled over, continuing to use it will "push" the thin edge down even harder.
Kind of like folding a piece of paper over then running your finger across the fold to realy set it down.
When you do that to steel, then try to straighten it, the thin edge (called a burr) can snap off.
Or - it can simply snap off itself from the pressure of being folded too tight.

There's a plethora of posts here where people report a joiner or planer blade getting a nick in it and swear to high heaven they did't hit anything hard duing the course of their work. My bet would be the burr edge simply folded down too hard and snapped off.

IMH - estimate 98% of steel edges are sharpened by needlessly removing material when all that's really needed is for the edge to be curled back to it's proper position.
That's all well and fine for a double bevel like a typical knife has, but not so practical for a chisel grind where the back edge needs dressed.
it's also not practical for the edges on saw teeth - or for most other (power) tool type blade applications.

Do a google search for the name Joe Talmadge.

Joe is to sharpening steel as Jeff Jewitt is to finishing and finishing materials. I've followed Joe's posts on several knife and custom knife forums for close to 10 years, and for a few years prior to that on the old news group alt.rec.knives.
He's written a lot of essays, magazine articles - and I believe he may have written a book on the subject also.